Physiologically important changes in metabolism, and morphology, occur during red blood cell maturation in both adult and maturing animals. Purine nucleotides, obligatory intermediates in energy metabolism, are potentially rate-limiting in these erythrocyte metabolic processes. Inasmuch as regulation of purine nucleotide turnover in red blood cells is not well understood, the quantitative determination of the mechanisms involved is crucial to a complete understanding of erythrocyte physiology. The long term objective of the proposed research is to define the modes of regulation of purine nucleotide metabolism in erythrocytes in mature and developing animals. Detailed studies of purine nucleotide metabolism in erythrocytes has been largely restricted to adult, mammalian systems. Few such studies have involved developing (maturing) systems. This lack of ontogenetic detail ignores the possibility that study and experimental manipulation of a dynamic developmental system may provide insights which are less readily apparent from studies of mature systems. It is apparent that AMP-deaminase is among those enzymes which are important in the regulation of purine nucleotide metabolism. A major omission in studies of AMP-deaminase (particularly in red blood cells) is the apparent lack of appreciation of its isoenzymic nature and the virtual absence of direct investigation of the structure and regulatory properties of purified individual isoenzymes. These investigations will include: purification of adult chicken erythrocyte deaminase to homogeneity; a systematic study of the catalytic properties of native and chemically modified isoenzymes of AMP-deaminase from adult chicken muscle and erythrocytes; structural studies (including molecular weights of intact enzymes and their subunits, amino acid compositions, terminal groups, and peptide maps); in vitro hybridization; investigation of the developmental increase in AMP-deaminase activity in erythrocytes with respect to the age of the animal and the state of red blood cell maturation (including manipulation of the pattern by experimentally induced anemia); investigation of possible changes in amount of enzyme by immunological methods; and comparison of the regulatory properties of erythrocyte deaminase from one-day-hatched and adult chickens.